The major objective of this investigation is to develop a new in vivo experimental approach for the examination of brain tissue metabolism. This new approach uses an intracarotid injection route to get radioactive compounds into the brain tissue of unanesthetized animals. To accomplish this, a segment of the common carotid artery is dissected free from connective tissue in the neck and surrounded with a flap of skin to form a carotid artery loop. After the operation, the carotid artery can be readily located and penetrated with a small gauge needle without anesthetizing the animal. Using this new in vivo approach, de novo glycerolipid synthesis will be evaluated in rat brain by determing te specific activity of the diglyceride pool in whole brain at 15, 30, 60 and 300 sec. following an intracarotid injection of equimolar amounts of (2-3H) glycerol and (3,4-14C) glucose into unanesthetized rats. An intraventricular injection route will also be utilized to determine; 1) if the total uptake of radioactivity into brain tissue is significantly altered when radioactive lipid precursors are injected into the cerebrospinal fluid system instead of the blood circulatory system, and 2) if the rate of de novo glycerolipid synthesis in brain tissue via the nonglycolytic pathway (as measured by (EH) incorporation into the diglyceride pool) or the glycolytic pathway (as measured by (14C) incorporation into the diglyceride pool) is significantly altered when two different injection routes are used to get (2-3H) glycerol and (3,4-14C) glucose into brain tissue. This new experimental approach should prove to be useful in determining the precise effect that drugs, ethanol, and physiological stimuli have upon the in vivo metabolism of brain tissue since; 1) unanesthetized animals can be used, 2) brain is the first tissue to be challenged with radioactive compounds, and 3) the uptake of radioactive compounds across the blood-brain barrier, which is the normal physiological route of entry for most compounds into brain tissue, can be accurately evaluated.